Among various Silicon on Insulation (SOI) approaches SIMOX (separation by oxygen implantation) seems to be the most promising as a replacement for use of silicon on sapphire (SOS) in CMOS processing. During the SIMOX process oxygen at the dose of about 1.0-2.0.times.10.sup.18 atoms cm.sup.-2 is implanted into a silicon wafer with energy of about 150-200 keV, at the temperature range of about 450.degree.-650.degree. C. To remove the implantation damage and to form a buried oxide, the SIMOX wafers are subsequently annealed at a temperature in the range from 1150.degree. to 1400.degree. C. A typical SIMOX structure is shown in FIG. 1 wherein a wafer 10 includes an oxygen implanted layer 12 and a regrown SIMOX film 14. A thin surface layer (.congruent.10-20 nm) of the SIMOX wafers serves as a seed during the solid state regrowth process. The degree of crystalline perfection of this layer will influence the crystallographic perfection of the regrown SIMOX film 14.
In order to predict the properties of SIMOX material after annealing that affect device performance, it is important to know the properties of the seed layer (degree of amorphism) after implantation. A second important parameter which will influence device performance is the roughness of the silicon surface. Faster erosion of silicon in the places exposed to hot spots in an ion beam could give a nonuniform, rough surface. A third important parameter which should be monitored is the presence of contaminations (e.g., carbon) which can form a thin film on SIMOX surfaces.
It would obviously be desirable to be able to examine a given SIMOX wafer and easily determine these three parameters, that is, amorphism, surface roughness, and surface contamination, prior to investment of substantial effort in the fabrication of integrated circuit devices. Methods have been developed which can be used to determine the crystalline quality of a semiconductor surface. Such a method is described in U.S. Pat. No. 4,352,016, which issued Sept. 28, 1982 to Duffy et al. Duffy et al. utilizes the reflections from two different wavelengths of light one of which is sensitive to both the physical and crystalline perfection of the surface being examined and the other of which is only sensitive to the physical perfection. By knowing the interrelationship between these two parameters and the reflectance characteristics of the surface for the particular wavelengths of light being used, the crystalline quality of the surface can be determined. Another method which utilizes reflectance of two different wavelengths of light is disclosed in U.S. Pat. No. 4,511,800 which issued Apr. 16, 1985 to Harbeke et al. Harbeke et al. chose the wavelengths of light so that the reflectance of one is sensitive to surface roughness while the other is sensitive to both the surface roughness and amorphism of the film being examined. Again, by knowing the interrelationship between these two parameters and the reflectance characteristics of the surface for the particular wavelengths of light being used, one or the other of the parameters can be determined.